In the art of oil field drilling technology, "directional drilling" is becoming increasingly prominent. In directional drilling, the angle of the borehole is altered during the drilling operation from vertical toward horizontal. Initially, directional drilling was developed in order to explore for oil under natural barriers, such as lakes. However, it has been determined that if the borehole passes along, rather than merely vertically traverses a permeable oil bearing formation, production can be dramatically increased.
It has been recognized that a number of advantages can be gained in drilling wells by employing a stationary drill pipe or drillstring which has attached, at its lower end, a downhole motor. The drive section of the downhole motor is connected to and rotates a drill bit. In such an apparatus, a fluid (such as air, foam, or a relatively incompressible liquid) is forced down the stationary drill pipe or drillstring and on passing through the fluid-operated motor causes rotation of a shaft ultimately connected to the drilling bit. The drillstring is held or suspended in such a manner that it does not rotate and therefore may be regarded as stationary. However, it is lowered in the well as the drilling proceeds.
In directional drilling, drilling motors are utilized wherein a bend may be located in the drillstring above the motor, a bend may be placed in the motor housing below the rotor/stator drive section, or the bit or output shaft can be angularly offset relative to the drive section axis.
In typical bottom hole assemblies (BHA), the motor, the motor housing, and the bit are placed below the MWD (measurement-while-drilling) sensors. These MWD sensors include accelerometers and/or magnetometers which are positioned in the MWD so as to form part of the bottom hole assembly. These sensors in the MWD can be used so as to determine the inclination and/or azimuth of the hole. Typically, the information from the MWD is transmitted to a surface location so that the position of the bit within the well bore can be properly determined.
In directional drilling applications, it is necessary to stop the rotating of the drillstring so as to properly take a measurement from the MWD. MWD measurements are not taken as the MWD section rotates with the rotating of the drillstring. Whenever the drillstring rotation is stopped, there is a tendency for the drillstring to contact the walls of the borehole. Such contact can occur from a buckling of the drillstring caused by the downward slide of the drillstring. Alternatively, the downhole formation can collapse inwardly onto the drillstring so as to create contact forces with the surface of the drillstring. In normal operation, when the rotation of the drillstring is stopped, the bit motor causes the bit to rotate and the drillstring slides downwardly so as to move the bit downwardly in the hole. If the drillstring should become "hung up" on the sides of the borehole, then the continued lowering of the drillstring will simply cause the drillstring to buckle. Drilling progress becomes rapidly inhibited by such contacts between the drillstring and the borehole wall. When the drillstring becomes stuck, it is necessary to lift the drillstring, to a certain extent, and to also rotate the drillstring so as to free the drillstring from the contact forces.
In the past, various patents have issued relative to directional drilling operations. U.S. Pat. No. 4,932,482, issued on Jun. 12, 1990 and U.S. Pat. No. 4,962,818, issued on Oct. 16, 1990, both to F. DeLucia teach a downhole motor with an enlarged connecting rod housing. A drill bit is connected to the lower end of the downhole motor and a bent sub is attached to its upper end. The downhole motor includes a motor housing, a connecting rod housing and a bearing housing. The connecting rod housing has a bend angle formed on the housing, which is enlarged to enable the connecting rod to be tilted at a larger angle than otherwise possible.
U.S. Pat. No. 5,022,471, issued on Jun. 11, 1991, to Maurer et al. teaches a deviated wellbore drilling system suitable for drilling curved wellbores which have a radius of curvature of approximately 10 to 1,000 feet. This system includes a drillstring, a drill bit, and a fluid-operated drill motor having a curved or bent housing section for rotating the drill bit independently of the drillstring. The drilling motor has an elongate tubular rotor/stator drive section containing a rubber stator and a steel rotor and the housing is bent or curved intermediate its ends. A straight or bent universal section below the bent rotor/stator section contains a universal joint for converting orbiting motion of the rotor to concentric rotory motion at the bit. A bearing pack section below the universal section contains radial and thrust bearings to absorb the high loads applied to the bits.
U.S. Pat. No. 5,094,305, issued on Mar. 10, 1992, to K. H. Wenzel teaches an orientable adjustable bent sub having a tubular member in the form of an adjustment sleeve, with a first end offset to a primary axis so as to telescopically receive the first end of the tubular member. By rotation of the adjustment sleeve, the offset portion of the adjustment sleeve is adjusted in relation to the offset portion of the tubular member so as to produce a bend of desirable magnitude. The adjustment sleeve is axially movable between an engaged position and a disengaged position.
U.S. Pat. No. 5,099,931, issued on Mar. 31, 1992, to Krueger et al. describes a method and apparatus for optional straight hole drilling or directional drilling in earth formations. This apparatus includes a downhole drilling assembly having a drill bit driven by a downhole motor and a deflection element in the assembly for imparting an angle of deflection to the drill bit relative to drillstring above the drilling assembly. At least two stabilization points for the drilling assembly in the borehole are used, with the drill bit, to define an arcuate path for the drilling assembly when the downhole motor is operating but the drillstring is not rotating.
German Patent No. 1,235,834, published on Mar. 9, 1967, describes a turbo-drill having a fixed shaft and a rotary body. A rotor and a stator form three differently sized groups so as to make up a turbo-convertor. Soviet Patent No. 832,016, published on Nov. 15, 1978, teaches a downhole motor for drills that has straight brake rim teeth with one tooth difference between rims for higher rotative moment on an output shaft. Soviet Patent No. 829,843, published on May 4, 1969 describes a turbodrill for downhole operations. This turbodrill has a flexible fluted ring received in a round stator boss groove to prevent twisting under blade reaction.
It is an object of the present invention to provide a method which allows the drillstring to be rotated independently of measurements carried out at the MWD.
It is another object of the present invention to provide a method that minimizes contact interference with the movement of the drillstring in the wellbore.
It is another object of the present invention to provide a method that reduces instances of drillstring buckling in the wellbore.
It is a further object of the present invention to provide a method for carrying out downhole measurements which allows for the adjustment of the tool face orientation without stopping the rotation of the drillstring.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.